Cranial bone defects caused by trauma, laceration or burns are challenging for aesthetically and functionally reconstruction surgeries [1, 2]. Implants for the reconstruction of these defects should offer different functions which could be realised by a hybrid construct with different layers.

Therefore, the aim of this project was to fabricate a titanium-hydrogel-hydroxyapatite hybrid structure, which mimics the biological and mechanical function, necessary to stimulate cranial bone formation, by three-dimensional (3D) bioplotting. Three layers consisting of a titanium mesh for the mechanical stability, an alginate soft layer to prevent fibroblast ingrowth and an alginate-hydroxyapatite (HA) layer for hard tissue reconstruction were combined.

The base - building platform of the construct - is a clinically used titanium mesh on which a dense and high concentrated alginate layer is plotted. Afterwards, porous structures of a composite material consisting of alginate and commercially available hydroxyapatite granules (average size 122 µm) were generated on top of the dense alginate layer. During the whole project the plotting process was optimised by several parameters, like pre-treatment of alginate and nozzle diameter of the used needles.

Finally, the constructs were characterised by applying different materials and cell biology methods.

It could be shown that alginate plotted on a titanium mesh exhibit strong mechanical and shape stability as well as little shrinkage, through improved pre-treatments. The optimised composition of alginate and HA (ratio of: 1:2) showed excellent printing results and microstructure analysis showed furthermore a homogenous distribution of HA particles inside the alginate matrix. Additional, first in vitro tests confirmed the cytocompatibility of the materials and structures.